[moderation] [ext4?] general protection fault in ext4_split_extent_at

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1c9982b49613 Merge tag 'drm-fixes-2026-03-14' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e35d52580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ccef46afa67b2b19
dashboard link: https://syzkaller.appspot.com/bug?extid=7e21644bab9e32cf125f
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1c9982b4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0ac9f4872167/vmlinux-1c9982b4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bdee9f3a13ab/bzImage-1c9982b4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7e2164...@syzkaller.appspotmail.com

EXT4-fs (loop0): pa ffff88804798e658: logic 0, phys. 209, len 19
EXT4-fs error (device loop0): ext4_mb_release_inode_pa:5465: group 0, free 0, pa_free 8
EXT4-fs error (device loop0): ext4_ext_split:1151: inode #18: comm kworker/u4:8: eh_entries 0 != eh_max 84!
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 1060 Comm: kworker/u4:8 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
RIP: 0010:ext4_split_extent_at+0x486/0xa40 fs/ext4/extents.c:3266
Code: 02 00 00 e8 0c 90 42 ff 49 bf 00 00 00 00 00 fc ff df 4c 8b 6c 24 38 0f b7 9c 24 e4 00 00 00 49 83 c4 04 4c 89 e0 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 23 05 00 00 66 41 89 1c 24 4c 8b 74 24
RSP: 0018:ffffc90001567180 EFLAGS: 00010247
RAX: 0000000000000000 RBX: 0000000000008004 RCX: ffff8880331d4980
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015672c8 R08: ffff888047a501d7 R09: 1ffff11008f4a03a
R10: dffffc0000000000 R11: ffffed1008f4a03b R12: 0000000000000004
R13: 1ffff920002ace44 R14: ffff8880368d5500 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff88808ca55000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007feb2c215ff8 CR3: 00000000123cf000 CR4: 0000000000352ef0
Call Trace:
<TASK>
ext4_split_extent fs/ext4/extents.c:3440 [inline]
ext4_split_convert_extents+0x36d/0x1a00 fs/ext4/extents.c:3830
ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3906 [inline]
ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3990 [inline]
ext4_ext_map_blocks+0xe70/0x58b0 fs/ext4/extents.c:4327
ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:809
ext4_convert_unwritten_extents+0x2be/0x5f0 fs/ext4/extents.c:5029
ext4_convert_unwritten_io_end_vec+0xff/0x170 fs/ext4/extents.c:5069
ext4_end_io_end+0xc7/0x410 fs/ext4/page-io.c:200
ext4_do_flush_completed_IO fs/ext4/page-io.c:291 [inline]
ext4_end_io_rsv_work+0x26a/0x340 fs/ext4/page-io.c:306
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_split_extent_at+0x486/0xa40 fs/ext4/extents.c:3266
Code: 02 00 00 e8 0c 90 42 ff 49 bf 00 00 00 00 00 fc ff df 4c 8b 6c 24 38 0f b7 9c 24 e4 00 00 00 49 83 c4 04 4c 89 e0 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 23 05 00 00 66 41 89 1c 24 4c 8b 74 24
RSP: 0018:ffffc90001567180 EFLAGS: 00010247
RAX: 0000000000000000 RBX: 0000000000008004 RCX: ffff8880331d4980
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015672c8 R08: ffff888047a501d7 R09: 1ffff11008f4a03a
R10: dffffc0000000000 R11: ffffed1008f4a03b R12: 0000000000000004
R13: 1ffff920002ace44 R14: ffff8880368d5500 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff88808ca55000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007feb2c215ff8 CR3: 00000000123cf000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
0: 02 00 add (%rax),%al
2: 00 e8 add %ch,%al
4: 0c 90 or $0x90,%al
6: 42 ff 49 bf rex.X decl -0x41(%rcx)
a: 00 00 add %al,(%rax)
c: 00 00 add %al,(%rax)
e: 00 fc add %bh,%ah
10: ff lcall (bad)
11: df 4c 8b 6c fisttps 0x6c(%rbx,%rcx,4)
15: 24 38 and $0x38,%al
17: 0f b7 9c 24 e4 00 00 movzwl 0xe4(%rsp),%ebx
1e: 00
1f: 49 83 c4 04 add $0x4,%r12
23: 4c 89 e0 mov %r12,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 0f b6 04 38 movzbl (%rax,%r15,1),%eax <-- trapping instruction
2f: 84 c0 test %al,%al
31: 0f 85 23 05 00 00 jne 0x55a
37: 66 41 89 1c 24 mov %bx,(%r12)
3c: 4c rex.WR
3d: 8b .byte 0x8b
3e: 74 24 je 0x64


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